The field of this invention is that of pressure sensors and the invention relates more particularly to a cylinder pressure sensor responsive to variations in pressure within a cylinder of an internal combustion engine to provide electrical signals corresponding to the pressure variations for use in regulating engine operation.
In commonly assigned U.S. Pat. Nos. 4,620,438 and 4,645,965, cylinder pressure sensing devices are shown to comprise a metal body for use in mounting a body of a pressure responsive ceramic piezoelectric material in sealed relation to an engine cylinder to be responsive to variations in cylinder pressure during engine operation to provide initial electrical signals representative of the pressure variations in the cylinder. Metal diaphragms and the like shield the piezoelectric materials from some aspects of the cylinder environments while transmitting pressure forces from the cylinders to the piezoelectric materials for generating the desired pressure responsive signals. In such known devices, electronic means are carried on the metal body for conditioning the initial electrical signals provided by the piezoelectric body for transmission to computer control means or other signal processing means at locations remote from the engine cylinder.
It is recognized that such cylinder pressure sensors will be subjected to applied pressures and operational temperatures which vary over wide ranges. The ceramic piezoelectric materials conventionally considered for use in such pressure sensors display substantial temperature dependence. Those materials are also found to display higher degrees of nonlinearity of response when they are employed at relatively high stress levels. It would be very desireable to provide a cylinder pressure sensor having improved linearity of response at the pressure and temperature levels likely to be encountered so that the initial signals provided by the sensor are more easily and economically conditioned for use in performing desired engine control functions and the like.